import sys
from PyQt5.QtWidgets import QMainWindow, QApplication
from PyQt5.QtGui import QIcon

class FirstMainWin(QMainWindow):
    def __init__(self,parent=None):
        super(FirstMainWin, self).__init__(parent)

        self.setWindowTitle('第一个主窗口应用')
        self.resize(400,300)
        self.status = self.statusBar()
        self.status.showMessage('只存在5秒的消息',5000)

if __name__=='__main__':
    app = QApplication(sys.argv)

    main = FirstMainWin()
    main.show()

    sys.exit(app.exec_())